Kids are kids the world over. I'm sure they knew what it was but maybe didn't fully realise the danger. I read only recently about a young lad who took a live WWII vintage hand grenade to school for a history project. I think it belonged to his Dad or more likely his Grandad. When his teacher saw it they evacuated the school & called in the Bomb Disposal Squad who took it away & blew it up.
Poor little lad...
I bet he got a telling-off from his Dad for allowing his grenade to be destroyed by the bomb squad...!
We had a WWII grenade which my Dad collected...
It was empty of explosives, and had the fuse removed...completely harmless...
It was an ornament on the mantelpiece...

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My Dad would have cancelled my copy of the Beano if I had taken it to school, and got it blown up...

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LOL...!
Paul...still reading the Beano...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.